Elastic wave device including a supporting substrate, medium layer, and piezoelectric body

Abstract

An elastic wave device includes a medium layer, a piezoelectric body, and an IDT electrode that are disposed on a supporting substrate. The medium layer is made of a medium containing a low-velocity medium in which a propagation velocity of a same bulk wave as that which is a main vibration component of an elastic wave propagating in the piezoelectric body and being used is lower than a propagation velocity of the elastic wave, and a high-velocity medium in which the propagation velocity of the same bulk wave as that which is a main vibration component of the elastic wave is higher than the propagation velocity of the elastic wave.

What is claimed is:  
     
       1. An elastic wave device comprising:
 a supporting substrate; 
 a medium layer stacked on the supporting substrate; 
 a piezoelectric body which is stacked on the medium layer and in which a bulk wave propagates; and 
 an IDT electrode disposed on a surface of the piezoelectric body; wherein 
 the medium layer includes a low-velocity medium in which a propagation velocity of a same bulk wave as that which is a main component of an elastic wave propagating in the piezoelectric body is lower than an acoustic velocity of an elastic wave propagating in the piezoelectric body, and a high-velocity medium in which the propagation velocity of the same bulk wave as that which is the main component of the elastic wave propagating in the piezoelectric body is higher than the acoustic velocity of the elastic wave propagating in the piezoelectric body; and 
 the medium layer is configured such that an acoustic velocity of a main vibration mode in the elastic wave device including the medium layer satisfies a relationship V L  <acoustic velocity of main vibration mode <V H , where V H  is an acoustic velocity of the main vibration mode in a case in which the medium layer is made of the high-velocity medium, and V L  is an acoustic velocity of the main vibration mode in the case in which the medium layer is made of the low-velocity medium. 
 
     
     
       2. The elastic wave device according to  claim 1 , wherein a dielectric constant of the medium layer is lower than a dielectric constant of the piezoelectric body. 
     
     
       3. The elastic wave device according to  claim 1 , wherein the medium layer is made of a composite medium including a mixture of the low-velocity medium and the high-velocity medium. 
     
     
       4. The elastic wave device according to  claim 3 , wherein the acoustic velocity of a bulk wave component that propagates in the medium layer and that is the same bulk wave which is a main propagation mode of an elastic wave propagating in the piezoelectric body is a value between an acoustic velocity of the bulk wave propagating in the high-velocity medium and an acoustic velocity of a bulk wave propagating in the low-velocity medium. 
     
     
       5. The elastic wave device according to  claim 4 , wherein a dielectric constant of the medium layer is lower than a dielectric constant of the piezoelectric body. 
     
     
       6. The elastic wave device according to  claim 3 , wherein a dielectric constant of the medium layer is lower than a dielectric constant of the piezoelectric body. 
     
     
       7. The elastic wave device according to  claim 1 , wherein the medium layer is defined by a multilayer body including a low-velocity medium layer made of the low-velocity medium and a high-velocity medium layer made of the high-velocity medium. 
     
     
       8. The elastic wave device according to  claim 7 , wherein the multilayer body includes at least three layers stacked on each other. 
     
     
       9. The elastic wave device according to  claim 8 , wherein a dielectric constant of the medium layer is lower than a dielectric constant of the piezoelectric body. 
     
     
       10. The elastic wave device according to  claim 7 , wherein a dielectric constant of the medium layer is lower than a dielectric constant of the piezoelectric body. 
     
     
       11. The elastic wave device according to  claim 7 , wherein, in the medium layer defined by the multilayer body, the low-velocity medium layer is disposed closer to the piezoelectric body than the high-velocity medium layer. 
     
     
       12. The elastic wave device according to  claim 1 , wherein the acoustic velocity of a bulk wave component that propagates in the medium layer and that is the same bulk wave which is a main propagation mode of an elastic wave propagating in the piezoelectric body is a value between an acoustic velocity of the bulk wave propagating in the high-velocity medium and an acoustic velocity of a bulk wave propagating in the low-velocity medium. 
     
     
       13. The elastic wave device according to  claim 12 , wherein a dielectric constant of the medium layer is lower than a dielectric constant of the piezoelectric body.